1. Field of the Invention
The present invention concerns a heat processing apparatus using liquefied gas, for example, butane gas as a fuel gas and, particularly, it relates to a heat processing apparatus using liquefied gas and having piezoelectric ignition means.
2. Description of the Prior Art
Heat processing apparatus in which catalytic combustion is taken place for a gas mixture comprising liquefied gas and air and piezoelectric ignition means is used for the ignition of the gas mixture have generally been known, for example, as described in U.S. Pat. No. 4,133,30l Japanese Patent Publication No. Sho 55-46783).
By the way, combustion catalysts comprising catalyst ingredients carried on fiberous ceramic supports have usually been employed in the conventional heat processing apparatus of the afore-mentioned type for facilitating the ignition by piezoelectric ignition means. However, such combustion catalysts involve a problem that they are damaged by burning in a short period of time by the heat during combustion.
In view of the above, it is necessary to support the catalyst ingredient, for example, on a solid support having a sufficient wall thickness, but since such a solid catalyst can not be heated to a temperature required for the oxidizing reaction merely by ignition sparks of the piezoelectric ignition means, it is necessary to once ignit the gas mixture by piezoelectric ignition means or by an external lighting means (as disclosed in our prior U.S. Pat. No. 4,552,124), to cause combustion with a pilot flame (hereinafter referred to as flaming combustion) so that the combustion catalyst can be heated sufficiently by the heat of the gas flame.
Referring to the piezoelectric ignition, in a case where an iron tip member having a built-in combustion catalyst is disposed at the top end (downstream end in the direction of the gas stream) of a cylindrical flaming combustion chamber and a gas mixture jetted out to the inside of the flaming combustion chamber is ignited by piezoelectric ignition means for flaming combustion, the entire amount of gases in the flaming combustion chamber (the including gas mixture supplied and combustion exhaust gases formed) is discharged through the inside of the iron tip member to the outside. Accordingly, if the size of the iron tip member is small, or no sufficient combustion space can be ensured at the inside of the flaming combustion cylinder even if the size of the tip member is large, the gas mixture is over-charged, in other words, a smooth gas flow is hindered in the flaming combustion chamber failing to ignit the gas mixture.
Further, even when the gas in the flaming combustion chamber is discharged smoothly, if the amount of the gas mixture is increased and thus the flow velocity of the gas mixture is increased near the ignition electrode, ignition to the gas mixture is not easy and it is extremely difficult, particularly, during severely cold winter seasons, etc.
There is also a problem upon extinguishing a once ignited flame. Although it is necessary to put off the pilot flame after the temperature of the combustion catalyst has been elevated to the oxidizing reaction temperature by the heat of the flame in order to improve the heat efficiency and ensure safety, as well as to prevent the thermal degradation of the catalyst by the flame, the flame can not easily be extinguished if the flow rate of the gas mixture is great.